Liquid aqueous synthetic organic detergent compositions have long been employed for human hair shampoos and as dishwashing detergents for hand washing of dishes (as distinguished from automatic dishwashing, machine washing of dishes). Liquid detergent compositions have also been employed as hard surface cleaners, as in pine oil liquids, for cleaning floors and walls. More recently, they have proven successful as laundry detergents too, apparently because they are convenient to use, are instantly insoluble in wash water, and may be employed in "pre-spotting" applications to facilitate removal of soils and stains from laundry upon subsequent washing. Liquid detergent compositions have comprised anionic, cationic and nonionic surface active agents, builders and adjuvants including, as adjuvants, lipophilic materials which can act as solvents for lipophilic soils and stains. The various liquid aqueous synthetic organic detergent compositions mentioned above serve to emulsify lipophilic materials including oily soils in aqueous media, such as wash water, by forming micellar dispersions and emulsions.
A cleaning action can be regarded as a more-or-less complex process resulting in the removal of soils from a given surface. The driving forces generally involved in this process are mechanical energy (friction, attrition, sonification, etc.), solvation by a liquid, thermal agitation, soil-solvent interfacial tension reduction, chemical modifications (caustic, acidic, oxidative, reductive, hydrolysis, assisted or not by catalysts or enzymes), soil or soil residual suspension (e.g. in micellar solutions), and so on.
When the cleaning action takes place in water liquid vehicle, auxiliary cleaning agents, especially surfactants, are generally required to get rid of hydrophobic soils. Moreover, in most domestic cleaning tasks, the success of the cleaning mechanism is based on the reduction of the water/oil interfacial tension. The generally admitted theory is that the oily soil is easily dispersed or even solubilized in the composition because of the low interfacial tension existing between the composition and the oil.
Another explanation can be evoked. Due to the low interfacial tension, the liquid detergent composition easily diffuses through the soil or between the support and the soil, thereby weakening all bonding forces; the soil is then spontaneously removed from the substrate. This is the cause for the removal of oily soil without a real solubilization of the soil which eventually is emulsified. Both mechanisms are complementary in the cleaning process.
Although emulsification is a mechanism of soil removal, it has been recently discovered how to make microemulsions which are much more effective than ordinary emulsions in removing lipophilic materials from substrates. Such microemulsions are described in British Patent Specification No. 2,190,681 and U.S. Pat. Nos. 5,082,284; 5,076,954 and 5,108,643 most of which relates to acidic microemulsions useful for cleaning hard surface items such as bathtubs and sinks, which microemulsions are especially effective in removing soap scum and lime scale from them. In U.S. Pat. No. 5,108,643 the microemulsions may be essentially neutral and as such are also thought to be effective for microemulsifying lipophilic soils from substrates. In U.S. Pat. No. 4,919,839 there is described a light duty microemulsion liquid detergent composition which is useful for washing dishes and removing greasy deposits from them in both neat and diluted forms. Such compositions include complexes of anionic and cationic detergents as surface active components of the microemulsions.
The various microemulsions referred to include a lipophile which may be a hydrocarbon, a surfactant which may be an anionic and/or a nonionic detergent(s), a co-surfactant which may be a poly-lower alkylene glycol lower alkyl ether, e.g. tripropylene glycol monomethyl ether, and water.
Although the manufacture and use of detergent compositions in microemulsion form significantly improves cleaning power and greasy soil removal, compared to the usual emulsions, the present invention improves them still further by the formation of aqueous near tricritical cleaning compositions which have improved cleaning as compared to microemulsions.
The instant aqueous cleaning compositions, which are optionally surfactant-free, provide increased grease and tar removal capabilities without or with a minimum mechanical action as compared to the water-based microemulsions as disclosed in U.S. Pat. Nos. 5,075,026, 5,108,643; 4,919,839 and 5,082,584. These water-based microemulsions all contain a surfactant as compared to the preferred surfactant-free compositions of the instant invention.
In most domestic cleaning tasks, the success of the cleaning mechanism is based on reduction of the water/oil interfacial tension. In this frame, the thermodynamic of phases predict that ultra-low interfacial tensions can be reached in the direct vicinity of peculiar compositions called "critical points" and particularly near "tricritical points," the properties of which were extensively described by Griffiths (Robert B.) Wheeler (John C.). Critical points in multicomponent systems, Phys. Rev. A, NEW YORK 1970, 2, (3), (Sept.), pp.: 1047-1064; and Griffiths (Robert B.). Thermodynamic model for tricritical points in ternary and quaternary fluid mixtures. J. Chem. Phys., LANCASTER. 1974, 60, (1), pp.: 195-206; and Widom. B. Tricritical points in three- and four-component fluid mixtures J. Phys. Chem., WASHINGTON. 1973, 77, (18), pp.: 2196-2200; and Widom (B.,) Interfacial tensions of three fluid phases in equilibrium. J. Chem. Phys. Lancaster, 1975, 62 (4) pp: 1332-13360 and Lang (J. C.) Widom(B.) Equilibrium of three liquid phases and approach to the tricritical point in benzene-ethanol-water-ammonium sulfate mixtures. Physica A, AMSTERDAM. 1975, 81A, pp.: 190-213; and Widom (B.) Three-phase equilibrium and the tricritical point. Kinan, MEXICO. 1981,3, A, pp.: 143-157
It must be pointed out that, in such critical compositions, surfactants are not a must. Moreover, it is not absolutely essential to be right at a tricritical point to obtain surface tensions much lower than those currently achieved with today's cleaning systems.
It is worthwhile to note that the tricritical points theory has already been under high scrutiny in view of enhancing oil recovery. These works are extensively described by Fleming (P. D.) Vinatieri (J. E.). Phase behavior of multicomponent fluids. J. Phys. Chem., WASHINGTON. 1977, 66, (7), pp.: 3147-3154 and Vinatieri (James E.) Fleming (Paul. D.). Use of pseudocomponents in the representation of phase behavior of surfactant systems. Soc. Pet. Eng. J., DALLAS, 1979, 19, pp.: 289-300; and Fleming (Paul D.) Vinatieri (James E.). Quantitative interpretation of phase volume behavior of multicomponent systems near critical points. AlChE J., NEW YORK 1979, 25, (3), pp.: 493-502; and Fleming (Paul D.) Vinatieri (James E.). Role of critical phenomena in oil recovery systems employing surfactants. J. Colloid Interface Sci., NEW YORK. 1981,81, (2), pp.: 319-331; and Vinatieri (James) Fleming (Paul D.). Multivariate optimization of surfactant systems for tertiary oil recovery. Soc. Pet. Eng. J., DALLAS. 1981, (2), pp.: 77-88; and Smith (Duane. H.). Interfacial tensions near the tricritical points of classical liquids: experimental evidence for the validity of the prediction of critical scaling theory. J. Chem. Phys., LANCASTER 1986, 85, PP.: 1545-1558. and Smith (Duane H.). Tricritical points as an aid to the design of surfactants for low-tension enhanced oil recovery. AOSTRA J. Res., EDMONTON(Alberta) 1984, (4), pp: 245-265.
In 1926, Kohnstamm rose the theoretical possibility of a critical point "of the second order" in a ternary liquid mixture, a point at which three co-existing fluid phases merge and become identical, Kohnstamm.(Ph.). Handbuch der physik, 1926, Vol. 10, Kap. 4, Thermodynamik der Gemische, pp. 270-271, H. Geiger and K. Scheel (SPRINGER, BERLIN). Kohnstamm also stressed the extreme difficulty to find such a point.
The aqueous cleaning near tricritical point compositions of the instant invention are applicable for use in concentrated household care products and personal care products. The near tricritical point compositions of the instant invention comprise harmless ingredients. The instant near tricritical point compositions permit the preparation of cleaning or conditioning liquid products which are optionally surfactant-free.
In accordance with the present invention, a near tricritical point cleaning composition, suitable at room temperature or colder or at a higher temperature for pretreating and cleaning materials soiled with a lipophilic soil, comprises a polar solvent such as water, a water soluble or dispersible low molecular weight amphiphile, and a non-polar solvent, or weakly polar solvent wherein the three phases have merged into one continuum at the tricritical point. The invention also relates to processes for treating items and materials soiled with soils such as lipophilic soil, with compositions of this invention, to loosen and to remove without mechanical action such soil by applying to the locus of such soil on such material a soil loosening or removing amount of the tricritical point compositions of the instant invention.
The instant aqueous cleaning composition exists at or in the vicinity of the tricritical point which is the terminus of three lines of critical points. The tricritical point is a thermodynamical point at which all three co-existing phases become identical simultaneously. At the tricritical point, the interfacial tension between the merging phases of the polar solvent (water) and the low molecular weight amphiphile is substantially zero, and the interfacial tension between the merging phases of the low molecular weight amphiphile and non-polar solvent (oil) or a weakly polar solvent is substantially zero, and the interfacial tension between the polar solvent and the nonpolar or weakly polar solvent is substantially zero. Accordingly, the cleaning mechanism of the cleaning compositions of the instant invention is based on the reduction of the polar solvent/non-polar solvent interfacial tension as it approaches the value of zero.
The compositions of the instant invention have a phase inversion temperature (PIT) of about 0.degree. to about 80.degree. C., more preferably about 15.degree. to about 40.degree. C. The phase inversion temperature is the temperature at which there is an equal affinity of the low molecular weight amphiphile for water and for oil. It is the temperature at which the partition of the low molecular weight amphiphile between the water rich phase and the non-polar solvent phase or weakly polar solvent phase equals unity. That is, the weight fraction of the low molecular weight amphiphile in the water rich phase is equal to the weight fraction of the low molecular weight amphiphile in the non-polar solvent phase.
The tricritical point compositions have ##EQU1## wherein the weight fraction of the water is equal to (1-.gamma.) (1-.alpha.) (1-.epsilon.) and .alpha. is about 0.03 to about 0.50 more preferably about 0.05 to about 0.30, .gamma. is about 0.01 to about 0.40, more preferably about 0.03 to about 0.25, and s is about 0 to about 0.20, more preferably about 0.01 to about 0.05, wherein the additive is a water soluble additive, a polar co-solvent or an electrolyte.
The additives are water soluble molecules (electrolytes or organics) that are able to modify the structure of water so as to strengthen or disrupt the solvent structure. Addition of such chemicals will therefore modify the solubility of uncharged organic ingredients in water and, among others, of amphiphilic molecules. The above chemicals are divided into two classes: Salting-out (or kosmotropic) agents reinforce the structure of water and make it less available to hydrate organic molecules. (Salting-out and -in agents are also referred to as lyotropes and hydrotropes, respectively.) Salting-in (or chaotropic) agents, on the other hand, disorder the structure of water, thereby creating an effect comparable to "holes." As a consequence they increase the solubility of polar organic molecules in water.
In practice, lyotropic agents make water more incompatible with both oil and amphiphile. The result is a decrease of the PIT and an increase of the supertricritical character. The amount of low molecular weight amphiphile needed to "congregate" water and oil generally increases in the presence of salting-out agents. Hydrotropic agents have the opposite effects.